Field of the Invention
This disclosure relates to an image processing apparatus, a control method thereof, and a storage medium.
Description of the Related Art
Emphysema is a type of obstructive pulmonary (lung) disease. After progression of destruction of alveoli mainly caused by cigarette smoking, emphysema exhibits enlargement of airspaces. The number of emphysema patients has been on the rise in recent years.
For tests and diagnoses of emphysema, a method called spirometry, which is for measuring breathing capacity, is mainly used. Spirometry involves measuring the amount of air that is actually inhaled and exhaled. For patients with severe emphysema, this measurement may become painful as the ability to breathe decreases.
Accordingly, quantitative measurements using medical image data (which may hereinafter be also referred to as “CT image”) captured by an X-ray computed tomography (CT) apparatus have been proposed in recent years. “Guidelines for the diagnosis and treatment of COPD (chronic obstructive pulmonary disease), 2nd ed., The Japanese Respiratory Society, Medical Review Co., Ltd. (2004)” states that a technique called “Goddard method” in which the stages of emphysema progression are expressed in scores is particularly simple and has been widely used. Therefore, there has been a demand for analysis software that enables evaluation based on the Goddard method.
The evaluation based on the Goddard method uses cross-sections of three lung fields, an upper lung field (near the aortic arch), a middle lung field (at the bronchial bifurcation), and a lower lung field (1 to 3 cm above the diaphragm). For each of the right and left lungs, the ratio of the area of a low attenuation area (LAA) to the area of each of the three lung fields is expressed in a score, and the severity of the chronic obstructive pulmonary disease is determined on the basis of the sum of the resulting scores. Note that the LAA is a region having a CT number clearly lower than that of a normal lung field region in a CT image. Typically, a region having a CT number of −950 HU or less is regarded as an LAA.
The measurements made at the six points on the right and left described above do not fully determine the condition of the entire lungs that are vertically long organs. Besides the score evaluation at the six points described above, it may be necessary to provide a mechanism that allows a diagnostician to visually and intuitively determine how the condition develops in the body axis direction.